Medical Implant

ABSTRACT

The invention relates to a medical implant (1′) in the form of an elongated helix wherein at least one part of the helix is preformed in such a manner that it has a secondary structure of identically sized loops which it assumes during implantation at the placement site, with said structure in turn forming at the placement site during implantation a polyhedral tertiary structure, and the polyhedron being provided with at least one additional loop.

The invention relates to a medical implant in the form of an elongatedhelix wherein at least one part of the helix is preformed in such amanner that it has a secondary structure which it assumes duringimplantation at the placement site, with said structure in turn formingat the placement site during implantation a polyhedral tertiarystructure, with each face of the polyhedron being built up by a loop.

The invention, furthermore, relates to a device for the implantation ofsuch implants in body cavities and vessels.

Known in the art is the use endovascular techniques for the occlusion ofbody cavities or vessels such as arteries, veins, fallopian tubes orvascular deformities such as, for example, vascular aneurysms. In thiscase, the closure element (also termed occlusion means) is usuallyintroduced by means of an insertion aid through a catheter into thecavity to be occluded and deposited therein by means of one of variousknown techniques. The occlusion of the cavity finally is brought aboutby an embolus that forms as a result of the flow of blood slowing downin the cavity thus reduced in size or filled by the occlusion means.

It is furthermore known in the art to introduce a plurality offilamentous occlusion means, for the most part helixes or spirals ofstainless steel or platinum alloys, into vascular aneurysms, with saidmeans then assuming a random configuration and in this way occlude theaneurysm. The drawback of such a method is that the occlusion meansoften fill and stabilize the cavity only inadequately and it is quitedifficult to foresee the behavior of said means when assuming theirsuperimposed structures so that in the end the safety of the operationmay be at risk as a ‘stiletto effect’ cannot be ruled out and may evenentail wall ruptures.

In order to circumvent such disadvantages it is furthermore known tomake use of occlusion means made of shape memory materials, said meansassuming a defined secondary and/or tertiary structure when insertedinto the cavity to be occluded.

With a view to most effectively filling vascular aneurysms and at thesame time stabilizing the aneurysm wall it is thus known in this contextfrom WO 01/93937 to use an occlusion means made of a material havingshape memory properties, said means when inserted having the primaryform of an elongated filament that upon being inserted into the aneurysmto be occluded develops into a secondary structure forming six loops ofidentical size which together build up a three-dimensional tertiarystructure having the form of a cage or cube. Each of the loops thusforms a face of the spatial structure and in this way determines thesize of the structure.

This principle is also known from WO 03/017852 which provides forimplants that as soon as external constraints are removed assume aregular, meander-like secondary structure which in turn develops into aspatial tertiary structure taking for example the form of a geometriccage, cube, tetrahedron or prism.

Occlusion means of this kind are meant to stabilize the aneurysm wall sothat further filamentous occlusion means can be inserted subsequentlywithout running the risk of causing wall ruptures. Although suchocclusion means may be viewed as an improvement compared tonon-preformed occlusion means in that they provide increased safety ofoperation, imminent rupturing danger still exists however in areas ofthe aneurysm wall, in particular those adjacent to faces and vertices aswell as edges of the polyhedrons, especially as a result of theocclusion helixes subsequently inserted into the aneurysm. Moreover,because of the largely openly configured tertiary structure of suchocclusion means the subsequently inserted occlusion means or portions ofsuch occlusion means can only be prevented from exiting through the neckof the aneurysm primarily in the case of small-neck aneurysms.

In view of the disadvantages associated with the state of the art it isthus the object of the invention to provide an implant that furtherreduces risks for patients when body cavities and vessels have to beoccluded. Desirable characteristics in this context are an extensive anddense coverage of the wall of the aneurysm, close contact with theaneurysm wall, a reliable occlusion of the aneurysm neck and/orprevention of the ‘stiletto effect’.

According to the invention this objective is reached by providing amedical implant of the kind first mentioned above which is characterizedin that the polyhedron is provided with at least one additional loop.

The invention is based on findings proving that when a higher packingdensity of the polyhedron is achieved through the provision orarrangement of additional loops the wall rupturing risk diminisheswithout the maneuverability of the implant during placement beingimpaired significantly. Preferably, the additional loops have a slightlysmaller diameter than the loops building up the faces of the polyhedron.

In this case, the implant is preformed in such a manner that it assumesthe desired secondary and tertiary structure after it has been releasedfrom the constraints of the catheter. For this purpose, an elasticbiasing force is imprinted on the helix, but at least on the portionthat forms the polyhedron, in a manner known through prior arttechniques. Therefore, not before an external (thermal or mechanical)constraint is omitted does the implant abandon its elongated structureand forms into its predetermined three-dimensional tertiary structure.Such a mechanical constraint, for example, may be exerted by thecatheter or a retaining element embracing or being situated within thehelix. The thermal constraint may, for instance, be imposed bytemperature conditions prevailing in the catheter that differ from thoseencountered in the blood stream. Means and interrelations of this kindare sufficiently known to competent persons skilled in the art.

With aid of inventive implants preformed in the described manner it ispossible to achieve a dense and gentle filling of the cavity to beoccluded without the wall of the cavity having to serve as an abutmentwhen the desired three-dimensional structure is formed, which is thecase with non-preformed implants. The risk of causing wall ruptures canthus be minimized.

Especially suited for the creation of such an elastic biasing force arematerials having shape memory characteristics or materials havingsuperelastic properties which are capable of undergoing a temperature-or stress-induced martensitic transformation or a combination of both.Other materials lacking shape memory properties such as, for example,platinum alloys, especially platinum-iridium and platinum-tungstenalloys, also lend themselves to the formation of the inventive implants.

In this context the additional loop or further loops may be arranged inthe polyhedron on one or several faces of the polyhedron. For example,one or also several smaller sized loop(s) may thus be arranged within aface of the polyhedron formed by a larger loop. This leads to a denserpacking of the polyhedron faces and minimizes the risk of the adjacentvessel or aneurysm walls becoming ruptured through additionally insertedfilamentous occlusion means. Furthermore, the neck of the aneurysm canbe better occluded in this way so that there is lower risk thatadditionally inserted filamentous occlusion means may exit.

The additional loop or further loops may also be arranged on the edgesof the polyhedron to enable the polyhedron edges to become more denselypacked which yields the advantages referred to above with respect toadjacent aneurysm areas.

Moreover, the additional loop or further loops may be arranged in areasof the vertices of the polyhedron to enable these vertex locations tobecome more densely packed which also yields advantages as describedhereinbefore with respect to adjacent aneurysm areas.

The three above elucidated possibilities of arranging further loops arenot necessarily facultatively with embodiments featuring more than oneadditional loop but may also be adopted in a cumulative manner to createpackings of the polyhedron that are optimally adapted to the cavity tobe occluded. The objective in this way is to obliterate the neck of theaneurysm to prevent the spirals from being flushed out.

As per an expedient embodiment of the inventive implant the polyhedronis a regular or a semi-regular polyhedron. In the event of asemi-regular polyhedron the faces themselves are also built up bydifferently sized loops. Furthermore, loops of even smaller size may bearranged within the smaller polyhedron faces formed by smaller loops sothat the relevant faces can be provided with a denser packing. The abovedescribed steps aimed at achieving a denser packing in the areas ofvertices und/or edges may expediently be adopted in this case as well.

It is seen as particularly expedient here if the polyhedron is atetrahedron, a hexahedron (preferably a cube), an octahedron, adodecahedron or an icosahedron. In the framework of the presentinvention a tetrahedron is especially preferred.

The loops may be provided in the form of closed or open loops. In aclosed loop the proximal and distal ends of the filament portion formingthe closed loop intersect whereas such intersection or crossing does nottake place in open loops. Because of the increased stability of thetertiary structure formed by the loops it is considered advantageous ifat least one and preferably all of the loops are closed loops.

According to another preferred embodiment the size relation betweensmall and large loops ranges between 1:1.1 and 1:5, preferably 1:1.1 and1:4 and especially preferred 1:1.1 and 1:2. The sizing depends, interalia, on the arrangement of the loops at the faces/edges or vertices.The implant in this case may consist of loops of two or more differentsizes. If two loops are arranged on one face the size relation as a ruleranges between 1:1.1 and 1:2 with the diameter serving as referencedimension.

As per another preferred embodiment the implant comprises more than onesmaller loop. Particularly preferred in the interest of increasing thesafety of operations by providing a higher packing density is anumerical relation between smaller and larger loops of at least 1:1.

With a numerical relation between smaller and larger loops of 1:1 it ispreferred if the small and large loops are alternately arranged alongthe linear extension of the filament. This arrangement results in thesafety of the treatment being further enhanced because it greatlyimproves the maneuverability and, surprisingly, enables the implantedfilament to be partially retracted from the cavity and into the catheterfor repositioning purposes during placement without canting, knots orfailure of the filament occurring.

In accordance with an especially preferred embodiment a smaller closedloop is arranged in the polyhedron in each of the polyhedron facesformed by the large loops.

It is, furthermore, particularly beneficial if in the polyhedron betweeneach of two adjacent loops forming the faces at least one smaller loopeach (or may be even more loops) is arranged. The loops arranged betweeneach of two adjacent loops forming the faces of the polyhedron aresituated on the edges of the polyhedron in this case.

Moreover, it is especially advantageous if in all areas of thepolyhedron where in each case at least three the faces forming loopsadjoin at least one small loop each is arranged (or may be even moreloops). The loops arranged between each of at least three adjacent loopsforming the faces of the polyhedron are situated on the vertices of thepolyhedron in this case.

It is, moreover, particularly expedient if the polyhedron is atetrahedron, the faces of which being formed by one of the large loopseach, with one smaller loop being located in each larger loop in thiscase as well.

As per another preferred embodiment the polyhedron is a tetrahedron, thefaces of which being formed by one of the large loops each, with onesmaller loop being located between each of two large loops at one edgeof the tetrahedron each.

A preferred further embodiment relates to an inventive medical implantwherein the polyhedron is a tetrahedron, the faces of which being formedby one of the large loops each, with one smaller loop being locatedbetween each of three large loops at one vertex of the tetrahedron.

For the purpose of occluding aneurysms it is seen particularly expedientto use implants according to the invention, the polyhedrons of whichhave a diameter ranging between 0.5 and 30, preferably 1 and 25 andespecially preferred between 2 and 20 and in particular between 3 and 18mm.

It is furthermore advantageous if the polyhedron is of larger size thanthe volume of the body cavity (the so-called “therapeutic space”) forthe filling of which it is meant. This so-called ‘oversizing’ serves tostabilize the implant in the cavity to be occluded and in this wayprevents it from being displaced within or expelled in part orcompletely from the cavity. However, to prevent the thin-walledaneurysms from being ruptured it is nevertheless deemed expedient not toprovide for too great a size of the polyhedron in relation to therelevant therapeutic space. It is therefore considered beneficial if thediameter of the polyhedron is not sized greater than 2.5, preferably 1.1to 2 and especially preferred 1.2 to 1.5 times the diameter of the bodycavity it shall fill.

The implant according to the invention is thus particularly suited forthe occlusion of aneurysms having a therapeutic measure (that is adiameter) ranging between 0.4 and 40, preferably between 1.5 and 20 andin particular between 2 and 18 mm.

According to an expedient embodiment the filament (if only a portion ofthe filament is used to form the polyhedron than particularly thisportion) in its extended state has a length of between 50 and 600 andpreferably between 75 and 500 mm.

The inventive implant may comprise, for example, of a helix or spiralformed by means of at least a single wire or with the aid of acable-like structure formed by means of at least two wires.Configurations in the form of a helix or spring or cable-like structurethus offer advantages in that an enlarged surface is provided forthrombozation purposes. To achieve the same purpose furtherconfigurations of the helix can be put to use that are conducive to asurface enlargement, for example providing said helix with fiberspromoting the formation of thrombi.

The single or plurality of wires in this case expediently have adiameter ranging between 20 and 200, preferably between 30 and 100,especially preferred 50 and 70 and in particular between 55 and 65 μm.

In accordance with an expedient embodiment the helix or spiral has aninternal lumen that is closed off at least at the distal end. At theproximal end the lumen may be open or closed. A lumen open towards theproximal end is, for instance, expedient if a removable retainingelement is arranged in the inner lumen of the filament, said elementpreventing the previously imprinted secondary and tertiary structure tobe assumed as long as it is located inside the implant. Such a retainingelement has been disclosed via publication WO 03/041615, with expressreference being made here to its disclosure content.

It is, furthermore, expedient if the helix has an outer diameter ofbetween 0.1 and 0.5, preferably between 0.2 and 0.35 and especiallypreferred between 0.24 and 0.28 mm. The helix in this case is preferablydesigned as micro-helix or micro-spring comprising one or several wiresor as a cable-like structure consisting of more than one wire braided ortwisted together.

As per a further expedient embodiment at least one of the wires formingthe helix or the wire forming the helix is made of a platinum alloy,preferably a platinum-iridium or a platinum-tungsten alloy or a metalalloy having shape memory properties.

It may be expedient if a filamentous shaping element made of a metalalloy having shape memory properties passes through the helix along itslongitudinal axis. The shaping element serves to bring about thesecondary and tertiary structure of the implant having left thecatheter. In this embodiment the filament having been released from thecatheter adapts to the predetermined shape of the shaping element whichenables the envisaged three-dimensional tertiary structure to be formed.Such a shaping element, for example, has been disclosed in publicationWO 03/017852, with explicit reference being made here to its disclosurecontent.

This embodiment provides for the helix to be expediently designed ascable comprising several wires, one of which being the shaping element,and, especially preferred, as spiral or helix through which inner lumenthe shaping element, preferably a wire, extends. It is, furthermore,considered expedient with this embodiment if the spiral or helix or, incase the design provides for a cable, those parts of the cable which donot form the shaping element, are made of a material that does not haveshape memory properties. Particularly expedient in this case is aplatinum-iridium alloy.

The alloy having shape memory properties in this case is preferably atitanium- and nickel-containing alloy (also known under the name ofnitinol), an iron-based or copper-based alloy.

According to another preferred embodiment the filamentous shapingelement extending along the longitudinal axis of the helix has a taperedportion situated in its distal end area. In this area said shapingelement thus has a diameter smaller than the element diameter inproximal direction. Such a distal tapered portion causes the shapingelement to be softer and less stiff so that traumatizing risks are lessimminent in the event the distal end of the shaping element comes intocontact with the wall of the aneurysm. Said distally arranged taperedsection is provided because it was found that the total stiffness of ahelix through which a filamentous shaping element extends is for themain part due to the shaping element and only to a lesser extent to thehelix itself. The taper may, for example, extend from the distal tipover a length of approx. 20 mm and may have an incremental slope, butpreferably a continuous slope. All in all, the diameter of the shapingelement up to its distal tip preferably reduces to approx. 25 to 50% ofthe diameter existing in the remaining area.

Another expedient embodiment relates to an inventive medical implantwherein a filamentous retaining element made of a polymer material (inparticular a polyester or polyamide) or a metal wire without shapememory properties (in particular a medical stainless steel wire) passesthrough the helix along its longitudinal axis. The retaining element inthis case serves to maintain the elongated configuration (in this casethe retaining element expediently is made and consists of a metal wire,especially in combination with a helix made of a shape memory material)or secure the helix preventing it from being torn off during placement,in particular when repositioning is required. In the latter case,provision of the retaining element made of a polymer material and of thehelix made of a shape memory material or a platinum-tungsten alloy isdeemed particularly expedient. Because of its good supporting qualitiesinstrumental in improving the slidability of the implant using aplatinum-tungsten alloy material for the helix is especially preferred.

The present invention, furthermore, relates to a device for theplacement of implants into body vessels and cavities with an implant inaccordance with the invention and an insertion aid which is detachablyconnected to the proximal end of the implant.

The insertion aid in this case is preferably designed as a guide wirewhich expediently and at least in part has the form of a helix orspring. The dimensioning and selection of suitable materials issufficiently known to competent persons skilled in the art. For thispurpose and by way of example explicit reference is made to thedisclosure content of publications WO 03/017852 and WO 03/041615.

If the inventive implant is provided with a removable retaining elementit has, expediently, the form of an open tube through which theretaining element can be introduced in and removed from the implant.

For the purpose of placing the implant into the cavity to be occludedimplant and insertion aid are expediently connected with each other bymeans of a severance module. For electrolytic placement of the implantthe severance module is expediently provided with an electrolyticallycorrodible spot made of a suitable material, for example a corrodiblesteel alloy.

Moreover, in the implant according to the invention one or moreadditional severance modules may be provided and arranged in the helixproximal to the portion forming the polyhedron. This enables the innerhollow space of the polyhedron to be filled immediately after it hasbeen placed into the body cavity to be occluded. The filament segmentarranged between polyhedron and severance module may be elasticallypreformed itself so that it is capable of assuming or taking up adefined form or position within the polyhedron. Arranging severalseverance modules of this kind inside the helix enables helix segmentsthat can be variably sized to be introduced into the polyhedron lumen.For electrolytic placement of the implant the severance module isexpediently provided with an electrolytically corrodible spot orlocation.

It is also viewed expedient if the device in accordance with theinvention also comprises a catheter, a voltage source and a cathode,with the implant serving as anode and being longitudinally movable inthe catheter, and with the connection between implant and insertion aid(preferably the severance module) having an electrolytically corrodiblelocation so that the implant can be detached by electrolytic processeswhen in contact with a body fluid.

In the interest of high resistance against fracture or breaking and atthe same time aiding the detachment process the severance module has adiameter ranging between 30 and 150, preferably between 40 and 120 andespecially preferred between 50 and 100 μm. The electrolyticallycorrodible location in this case may have a smaller diameter than theadjacent proximal and distal areas of the severance module (theseverance module in this case tapers off towards the electrolyticallycorrodible spot).

The severance module is expediently provided with a proximal and adistal helix as well as a segment arranged in between, with the helixesconsisting of a material whose susceptibility to electrolytic corrosionis lower than that of the interposed segment. Suitable and expedientmaterial combinations are noble metals or noble metal alloys, preferablyplatinum or platinum alloys for the proximal helix or distal helix andstainless steel (e.g. grades AISI 301, 303 or 316 as well as subgroupsthereof or N-alloyed austenitic steel of stainless quality grade,preferably from the group of pressure-nitrided steels) for theinterposed segment. Material combinations of this type are also knownfrom WO 03/017852 to which reference is made here.

In accordance with an advantageous embodiment of the inventive devicethe severance module is non-detachably connected to the implant and theinsertion aid by welding, soldering, bonding or mechanical joiningprocesses, particularly by force- or form-closing methods in a mannerknown to persons skilled in the art.

As per another advantageous configuration of the inventive device theinsertion aid is surrounded, at least in part, by an electricallyinsulating shrunk-on sleeve or an electrically insulating coating.

Moreover, the purpose of the invention can be most beneficiallyaccomplished with the aid of a helix, the loops of which forming thefaces of a dodecahedron, in particular a regular pentagonaldodecahedron. Due to the plurality of faces—twelve altogether—a verydense coverage of the wall is achieved so that, as the case may be, evenwithout additional loops the aneurysm wall can be widely covered and anextensive obliteration of the neck of the aneurysm be brought about.

The helix designed and preformed so as to yield the shape of apentagonal dodecahedron thus forms a flexible skeleton covering andprotecting the wall, with said skeleton being capable of accommodatingand retaining further helixes serving occlusion purposes. In this casefurther loops often need no longer be arranged additionally on faces,edges or vertices. In this respect, measures promoting the slidingbehavior aimed at counteracting patient traumatizing risks can largelybe dispensed with.

Arranging the proximal end of the helix forming the pentagonaldodecahedron on a vertex or corner point was found to be particularlybeneficial. Since the neck of the aneurysm is usually located within aface of the polyhedron this makes it difficult for the last-insertedportion of the helix to slip out of the neck and helps to prevent thehelix from being flushed out which anyway is improbable due to theplurality of the faces, the close contact with the wall of the aneurysmand the strain that as a rule prevails inside the aneurysm. The distalend of the helix is preferably arranged in a face and is the point wherethe first loop starts; advantageously here is a mainly atraumaticsupporting location on a side facing away from the neck of the aneurysm.

The invention is now described by way of examples as follows withreference being made to the figures showing the respective embodiments.

FIG. 1 shows the enlarged representation of a cube-shaped implant 1 ofthe state of the art;

FIGS. 2 a and 2 b are the enlarged representations of an inventiveimplant 1′ with smaller closed-loops 8 arranged in the tetrahedron faces2′;

FIG. 3 is the enlarged representation of an inventive implant 1′ withsmaller closed-loops 8 arranged in the tetrahedron faces 2′, shown asdevelopment of a ball;

FIGS. 4 a and 4 b are the enlarged representations of an inventiveimplant 1′ with smaller closed-loops 8 arranged at the vertices 4′ of atetrahedron 6;

FIG. 5 is the enlarged schematic representation of an inventive implant1′ with smaller closed-loops 8 arranged at the vertices 4′ of atetrahedron 6, shown as development of a ball;

FIG. 6 is the enlarged vertical section of the inventive implant 1′positioned in an aciniform aneurysm 13;

FIG. 7 is the schematic representation of a development of an inventiveimplant in the form of a pentagonal dodecahedron; and

FIG. 8 shows the taper provided in the distal end area of a filamentousshaping element.

FIG. 1 represents a cube-shaped implant 1 of enlarged size reflectingthe state of the art. The open configuration, especially of the faces 2and vertex areas 4, but also of edges 3, is to be seen as a weak pointof such implants 1 because the aneurysm wall in contact with them isparticularly prone to rupture. In addition, the insufficient packingdensity of the implant 1 in the vicinity of said areas 2, 3 and 4 onlyprevents to a minor extent implants subsequently placed for the purposeof filling the inner hollow space 5 from being expelled again.

FIG. 2 shows two views 2 a and 2 b of a tetrahedron-shaped implant 1′according to the invention, said implant having assumed itsthree-dimensional tetrahedral tertiary structure. The faces 2′ oftetrahedron 6 are built up by two uniformly sized large loops 7, two ofwhich in each case being adjacently positioned, with the projections ofthe large loops 7 extending into the space constituted by the sectionalareas of two neighboring large loops 7 each forming the imaginary edges3′ of tetrahedron 6.

In each of faces 2′ a loop 8 of smaller size is arranged. By thisarrangement the packing density of the tetrahedron 6 in the area offaces 2′ is increased, which significantly improves the safety againstrupturing dangers to which the adjoining aneurysm wall is exposed whenimplant segments or further implants are subsequently inserted orplaced. The high packing density thus achieved in faces 2′ moreoverprevents in particular subsequently inserted implant segments orsubsequently inserted additional implants meant to fill the inner hollowspace 5′ from being forced out again through the neck of the aneurysm.For that reason the implant 1′ according to the invention isparticularly suited as well to the therapeutic occlusion of wide-neckaneurysms the treatment of which, as is known, is especially difficultas a rule.

Besides, the arrangement of the smaller loops 8 slightly raised abovethe projection plane of the tetrahedron faces 2′ formed by the largeloops 7 enables the implant 1′ to be particularly well secured in theaneurysm, with special reference in this context being made to FIG. 2 a.

Filament 9 forming the tetrahedron 6 is a micro-helix having a diameterof 0.26 mm and consisting of a platinum-iridium wire which has adiameter of 60 μm. A nitinol wire extends through the inner hollow spaceof the micro-helix, said wire being non-detachably connected at theproximal and distal end to filament 9 and due to its elastic biasingforce imprinting on the helix 9 the tetrahedral tertiary structure aftersaid helix has been released from the catheter.

FIG. 3 represents the secondary structure of the tetrahedron shown inFIG. 2 in the form of a development of a ball making use of 4 radialsections 10 to 10′″. The loops 7/8 themselves are of roughly circularshape and having assumed their predetermined spatial configuration forma regular tetrahedron. Along the longitudinal axis of helix 9 the large7 and the small loops 8 are arranged alternately, with the small loops 8being placed inside the large loops 7 in the secondary structure. Theproximal and the distal ends of filament 9 are identified by referencenumber 11 and, respectively, 12.

FIG. 4 shows two views 4 a and 4 b of a tetrahedron-shaped implant 1′according to the invention, said implant having assumed itsthree-dimensional tertiary structure. The faces 2′ of tetrahedron 6 arebuilt up by uniformly sized large loops 7 of which two each arepositioned adjacent to each other and thus form by way of theirprojections the imaginary edges 3′ of tetrahedron 6. At the locationwhere the projection of three adjoining large loops 7 each intersectsthere are the vertices 4′ of the tetrahedron, with one smaller sizedloop 8 each being arranged at said vertices. Since the smaller loops 8are arranged below the imaginary points of intersection the tetrahedron6 in this case has a more rounded shape deviating from an idealgeometric tetrahedron shape. By this arrangement the packing density ofthe tetrahedron 6 in the area of vertices 4′ is increased, whichsignificantly improves the safety against rupturing dangers to which theadjacent aneurysm wall is exposed when implant segments or furtherimplants are subsequently inserted or placed. Aside from this, therounded tetrahedral shape thus formed will more favorably adapt to theorganic structure of aneurysm lumens to be filled than could beaccomplished with an ideal geometric tetrahedron. The high packingdensity thus achieved at vertices 4′ moreover prevents in particularimplant segments or additional implants subsequently inserted or placedfor the purpose of filling the inner hollow space 5′ from being forcedout again through the neck of the aneurysm.

The helix 9 forming the tetrahedron 6 is a micro-helix having a diameterof 0.26 mm and consisting of a platinum-iridium wire which has adiameter of 60 μm. A polymer thread or a thread made of anickel-titanium alloy extends through the inner hollow space of themicro-helix, with said thread being fixed at the proximal and distal endof the helix 9 and prevents the helix 9 from being torn off during theplacement or repositioning. On the platinum-iridium wire an elasticbiasing force has been imprinted which forces it into its preformedtetrahedral configuration as soon as the mechanical constraint caused bythe catheter has been omitted. Although the platinum-iridium alloy usedhas no shape-memory properties it greatly improves the slidability ofthe helix during placement on account of its excellent supportingcharacteristics.

FIG. 5 by way of 4 radial sections 10 to 10′″ represents the secondarystructure of the tetrahedron shown in FIG. 4 in the form of thedevelopment of a ball. The loops 7/8 themselves are of roughly circularshape and having assumed their predetermined spatial configuration forma regular tetrahedron. Along the longitudinal axis of helix 9 the large7 and the small loops 8 are arranged alternately, with the small loops 8being placed between the large loops 7. The proximal and the distal endsof helix 9 are identified by reference number 11 and, respectively, 12.

In FIG. 6 an implant 1′ according to the invention is illustrated thatis placed into an aciniform aneurysm 13, said implant forming into atetrahedron 6 as tertiary structure. By arranging the smaller loops 8 inthe area of the faces 2′ of the tetrahedron 6 built up by the largeloops 7 a higher packing density of the tetrahedron faces 2′ isachieved. This not only reduces the danger of a wall rupture but alsoand in particular prevents additionally inserted implants (not shownhere) from exiting through the neck of the aneurysm 14. Thisconfiguration even enables aneurysms exhibiting medium-sized necks 14 asillustrated here to be occluded without having to employ stents. It isparticularly expedient here if the implant 1′ as shown is positioned insuch a way that one of the tightly packed face areas 2′ of thetetrahedron 6 is situated at or above the aneurysm neck 14.

The tetrahedral tertiary structure is excellently suited for theocclusion of large aneurysms, for example of an aneurysm 13 as shownhere having a therapeutic dimension of 10 mm in diameter. Since thetetrahedron 6 has a diameter of 12 mm it secures itself firmly insidethe aneurysm 13 during placement when forming into its tertiarystructure such that the tension thus built up prevents it from slippingout of the aneurysm 13. Such an “oversizing” offers advantagesparticularly for the treatment of wide-neck aneurysms because customaryimplants are not sufficiently secured inside of them to make sure theycannot exit or be expelled.

With the help of a micro-catheter the implant 1′ with the distal portion12 of the helix 9 in front was moved through the blood vessel 15 intothe aneurysm 13 where, when discharged from the catheter, it assumed theillustrated three-dimensional tertiary structure on account of a mixedstress- and temperature-induced martensitic transformation of thenitinol wire accommodated in the micro-helix 9 consisting of aplatinum-iridium alloy. After checking the correct positioning underradiographic control by employing customary state-of-the-art methods theimplant was detached electrolytically from the insertion aid designed inthe form of a guide wire. For this purpose and with the aid of a sourceof electrical power a voltage was applied for a period of 0.1 to 20minutes to the cathode positioned on the body surface and to the implant1′ acting as anode and being placed in the aneurysm 13 to be occluded.Applying this voltage resulted in the implant 1′ becomingelectrolytically detached due to electrolytic corrosion taking place atthe electrolytically corrodible location in the severance modulearranged between the guide wire and the filament 9. Said severancemodule is of particularly robust design and has a relatively largediameter of 100 μm to yield a high margin of safety preventing kinkingor buckling when the implant 1 is positioned. Finally, the guide wirewas retracted into the catheter and then removed from the systemtogether with the catheter.

FIG. 7 is a schematic view of the development of a pentagonaldodecahedron and the extension of a micro-helix 9 designed to form intoa pentagonal dodecahedron. The individual faces F1 to F12 of thepolyhedron are defined by the loops of the micro-helix. In this case thedistal end of the micro-helix 9 is located on a face F12 whereas theproximal end enters the body at a vertex or corner point betweenF1/F2/F3.

FIG. 8 eventually shows as schematic representation the tapered portionof the distal end 17 of a filamentous shaping element 16 reducing toapprox. 50% of the diameter.

1. A medical implant comprising: an elongated helix; at least one partof the helix preformed to define a secondary structure with loops ofsubstantially identical size during implantation at a placement site;said secondary structure forming at the placement site a polyhedraltertiary structure with each face of the polyhedron being built up by aloop, and the polyhedron provided with at least one additional loop. 2.Medical implant according to claim 1, characterized in that theadditional loop is arranged in an area selected from a polyhedron face,polyhedron edge, and a polyhedron vertex.
 3. Medical implant accordingto claim 1 characterized in that the polyhedron is selected from atetrahedron, a hexahedron, an octahedron, a dodecahedron, a pentagonaldodecahedron, and an icosahedron.
 4. Medical implant according to claim1, characterized in that the loops are closed loops.
 5. Medical implantaccording to claim 1, characterized in that the at least one additionalloop is smaller than the loops forming the polyhedron faces.
 6. Themedical implant according to claim 5, characterized in that thenumerical proportion between smaller and greater loops is approximately1:1.
 7. The medical implant according to claim 4, characterized in thatthe closed loops are alternately arranged in a linear extension of theelongated helix.
 8. Medical implant according to claim 7, furthercomprising characterized in that in the polyhedron a smaller looparranged in each of the polyhedron faces which are formed by the largeloops.
 9. Medical implant according to claim 7, characterized in that inthe polyhedron a small loop is arranged between two adjacent largeloops.
 10. Medical implant according to claim 7, characterized in thatin the polyhedron a small loop is arranged between three adjacent largeloops.
 11. Medical implant according to claim 1, characterized in thatthe size of the polyhedron is greater than the volume of the body cavitywhich it is meant to fill.
 12. Medical implant according to claim 1,characterized in that the elongated helix in extended state has a lengthranging between 50 and 600 mm.
 13. Medical implant according to claim 1,characterized by a microcoil having a lumen which is closed at least ata distal end thereof.
 14. Medical implant according to claim 1,characterized in that the elongated helix has an outside diameterranging between 0.1 and 0.5 mm.
 15. Medical implant according to claim1, characterized in that at least one of the wires forming the elongatedhelix comprises one of a platinum-iridium and platinum-tungsten alloyhaving shape memory properties.
 16. Medical implant according to claim1, characterized in that a filamentous shaping element made of a metalalloy having shape memory properties passes through the elongated helixalong a longitudinal axis thereof.
 17. Medical implant according toclaim 16, characterized in that a filamentous retaining element (16)made of a polymer material or a metal wire without shape memoryproperties passes elongated helix along a longitudinal axis thereof. 18.The medical implant according to claim 16, characterized in that thediameter of the filamentous shaping element (16) reduces towards adistal end thereof.
 19. Medical implant according to claim 18,characterized in that the diameter of the filamentous shaping element(16) at the distal end amounts to 25 to 50% of a remaining diameter ofthe shaping element.
 20. The medical implant according to claim 18,characterized in that the diameter of the filamentous shaping elementconstantly narrows in the range of the distal end.
 21. Medical implantaccording to claim 1 further comprising at least one severance moduleprovided with an electrolytically corrodible location which is arrangedin the elongated helix proximally to a portion thereof forming thepolyhedron.
 22. A medical implant according to claim 1 in combinationwith an insertion aid which is detachably connected to the proximal end(11) of the implant.
 23. The combination according to claim 22comprising a catheter, a voltage source and a cathode, with the medicalimplant serving as an anode and being longitudinally movable in thecatheter, with the connection between the medical implant and theinsertion aid having an electrolytically corrodible location so that themedical implant can be detached by an electrolytic processes when incontact with a body fluid.
 24. The combination according to claim 23,characterized in that the insertion aid has the form of a guide wire.25. The combination according to claim 24, characterized in that theguide wire has, at least in part, the form of one of a helix and aspring.
 26. The combination according to claim 25, characterized in thatthe medical implant and the insertion aid are connected with each otherby means of a severance module provided with an electrolyticallycorrodible location.
 27. The combination according to claim 26,characterized in that the severance module is provided with a proximaland a distal helix as well as a segment arranged in between, with thehelixes consisting of a material whose susceptibility to electrolyticcorrosion is lower than that of the interposed segment.
 28. Thecombination according to claim 27, characterized in that the severancemodule is non-detachably connected to the medical implant and theinsertion aid by a process selected from welding, soldering, bonding,mechanical force closing and mechanical form-closing.
 29. Thecombination according to claim 23, characterized in that the insertionaid is at least partially surrounded, by one of an electricallyinsulating shrunk-on sleeve and an electrically insulating coating.